This is a comment on WUWT that I’m preserving here since I’m tired of needing to explain this again and again and look up the book reference each time.
E.M.Smith March 20, 2015 at 1:52 pm Edit
Yes! (To Slavatore Del Prete)
This (from a paper trying to say it was CO2, not orbital cycles, that cause the ice age / interglacial cycles):
“This makes sense in that the whole world was cold at the same time, but the Milankovitch theory should have opposite effects for the Northern and Southern Hemispheres, and thus cannot explain the synchronous advance of glaciers around the globe. ”
Is where they have gone idiotically wrong. You, Salvatore, and Data Soong, have got it right.
“They” have made the typical “noob” idiot mistake of simplification and leap to conclusion. Had they actually read about the Milankovitch cycle hypothesis they would have enough clue to know they were being idiotic.
The “thumbnail” is that first Milankovitch thought something similar, but found the data conflicted. Then he tried another approach that also failed as it was “exactly backwards”. Then he had the “Ah Ha!” moment and got it right. It is all neatly described in a history of his work that I’ll recommend below. But first:
The basic cause of the asymmetry is the land. The South Pole is all land all the time surrounded by water. The North Pole is all water all the time surrounded by land. Due to this, the South Pole is ALWAYS frozen. Always. Full stop. No melting. Done deal. (Anyone talking about the South Pole “melting” is full of it. No other option applies.) Only the North Pole can melt.
And melt it does, but ONLY when things are just EXACTLY right. We are, fundamentally, an Ice Age Planet that pops out of it just for a tiny little while and only when things are just right to melt the north pole ice. Anyone who is all worked up that the North Pole is melting is like the dog trying to sink his teeth into a car tire doing 30 MPH. If he gets what he wants he will be seriously injured and absolutely mortified. WHEN the North Pole freezes over next and stays frozen we are headed head first into that long night of deep freeze frozen ice age “pronto” with no recourse. Again: Period, full stop.
What Milankovitch figured out was that when ALL the parameters of the Earth Orbit line up just so, we barely cross the threshold for North Pole melting and poke our little frozen noses out for just a little while. Then when any of them gets far enough away from that magic alignment, it’s all ice ice baby all the time again. We are presently on the cusp of that W/m^2 rate and can be stable in either frozen or melted states depending on albedo of snow on the ground…
One other point, the key bit is NOT distance from the sun. In fact, we melt when furthest from the sun. Solar energy is not diminished worth note by distance, BUT when the Earth is at it furthest from the sun, it takes longer to make the season change happen. So when it is summer at furthest from the sun we have a few more days of summer. It is that few more days, not the simple W/m^2, that melt things and let the interglacial happen.
So, when summer in the Northern Hemisphere happens with the Earth furthest from the sun, and the tilt is maximized so polar heat is maximized, and the orbital eccentricity is maximum so we get the most added days of N.H. summer, then, and only then, can ONE pole melt, that being the N.H. pole, and allow an interglacial. At all other configurations we freeze.
(Sidebar per the 41K / 100K year problem: IMHO it is pretty easy to explain. In the past we were warmer. We could melt the north pole on lesser changes, like the 41 ky changes alone. Now we are, overall, much colder. It takes ALL the parameters being neatly aligned and that only happens on the 100 Kish year cycle. Really about 120 ky including the interglacial part… Look at the temp record and you can still see spikes up at the 41 ky cycle points, just not enough to melt the North Pole…)
FWIW, if you would understand the actual Milankovitch theory (which is unlike what most folks think it is and post about and complain about and…) there is a very nice small and readable book that explains it all nicely. It is the story of the history of Milankovitch and his work with paper and pen while in a German prison, only incidentally going into the theory and how it works, via relating what he tried and failed and tried again until he got it right. That book is highly recommended:
“Ice Age: The Theory That Came In From The Cold!” by John and Mary Gribbin.
Please, buy it and read it. It’s a wonderful tale and full of useful information for the small size and only 105 pages. You will never look at Milankovitch the same way again once you know about his life and how carefully he worked all this out. Spending, literally, years in a prison cell with plenty of time to think and nothing but pen and paper to do the work. (The Germans in that WW were not fond of his nationality…) At the end you will understand just how interglacials form, and why they are the key bit, not “why ice ages happen”… we are default ice…
If the warmistas had a clue about this they would be actively praying for “global warming”. In no more than 2000 years and potentially as short as 300 years you can kiss Canada good-by as the ice returns. New York City goes too, but a bit later as the ice takes a while to build up… And there is absolutely nothing we can do to stop it.
Now, back at this “paper”…
As they have already got it entirely wrong by saying that the hemispheres ought to be counter cyclical to each other (and completely do not have a clue that Milankovitch took that approach, found it wrong – provably – and discarded it) and are clueless about what Milankovitch actually SAID causes interglacials, the rest of their work is disposed of in the same trash barrel. If you can’t even check your references and read your citations, the rest is going to be garbage…